Problem is the same tracking data can and is used for different purposes. I agree that usage analytics can be really helpful to site owners/developers/maintainers to improve the site and give visitors a better experience. For that, anonymous data might suffice. The visitors benefit from this and many visitors would certainly be able to accept such use.
However, when the same data is also used for targeted advertising (where the ads also pose a security risk!), extensive mapping and profiling through syncing with other data, etc., by the site owner or more frequently by the tracking service provider (Google and others), then many quite rightly feel that they want to protect themselves.
Because visitors can not control how tracking data is used, they are forced to block everything. And as long as they are not given better control over the use, it is quite reasonable that they are allowed to make that choice. And that it is respected.